Wet-end manufacturing process for bitumen-impregnated fiberboard

ABSTRACT

A process for manufacturing fiberboard by preparing a fiber slurry mixture including containing cellulose fibers and water then atomizing a liquid bituminous material, such as asphalt. The liquid bituminous material is atomized by mixing it with a pressurized gas, such as compressed air, forming a mist comprising droplets of bituminous material having a diameter between 20 microns and 50 microns. A water spray solidifies the bituminous material droplets thereby forming bituminous particles which fall into the fiber slurry within the spray chamber. From there the slurry is sheared, dewatered, and dried, forming a finished fiberboard.

RELATED APPLICATIONS

This application claims priority to, and is a continuation of, U.S.application Ser. No. 13/248,758, having a filing date of Sep. 29, 2011,which is incorporated herein by reference, and which claims priority to,and is a continuation of, U.S. patent application Ser. No. 12/881,721,having a filing date of Sep. 14, 2010, now U.S. Pat. No. 8,038,845,which is also incorporated herein by reference in its entirety, andwhich claims priority to, and is a divisional of U.S. patent applicationSer. No. 12/200,993, having a filing date of Aug. 29, 2008, now U.S.Pat. No. 7,815,772, which is also incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

The present disclosure relates to a process for manufacturing fiberexpansion joints. In particular, the present disclosure relates to amethod for introducing fine particles of bituminous material, such asasphalt, into a slurry fiber mixture for formation into boards used infiber expansion joint applications. Although the term “asphalt” is usedthroughout the present disclosure, it should be understood that anybituminous material, including tars and pitches, may be employed andstill remain within the scope of the present disclosure.

Asphalt impregnated expansion joints are used in connection withconcrete structures to relieve stresses created by thermal expansion andcontraction of the concrete and prevent failure of the concrete causedby changes in ambient temperature. Typical applications for asphaltimpregnated fiber expansion joints include sidewalks, driveways, floorslabs, streets, highways, airport runways, and similar applications.Because such concrete expansion joints are installed in applicationsexposed to the weather, it is desirable that water absorption be limitedto prevent degradation of the expansion joint. It is also desirable thatconcrete expansion joints have strength and resiliency. Therefore,asphalt impregnated fiberboard expansion joints are required to meet orexceed the requirements of ASTM Standard Specification D 1751-04.

ASTM D 1751-04 requires that an expansion joint for concrete paving andstructural applications have specified material characteristics,including that 35% weight of the finished fiberboard shall be asphaltuniformly distributed throughout the board. Additionally, the stressrequired to compress a test specimen of a fiber expansion joint to 50%of its original thickness must not be less than 100 psi nor greater than750 psi. When a fiber expansion joint is compressed to 50% of itsoriginal thickness having three of its edges restrained, the amount ofextrusion of the free edge cannot exceed 0.25 inch. A fiber expansionjoint that has been compressed to 50% of its original thickness mustrecover at least 70% of its thickness within 10 minutes after theapplied load is released. A fiber expansion joint must not have adensity less than 19 lb./cu. ft. A fiber expansion joint test specimenwith four square-cut edges, when submerged horizontally under 1 inch ofwater at 70 degrees F. may not absorb more than 15 volume % in 24 hoursfor a nominal volume of ½ inch and no more than 20 volume % for allother thicknesses.

Fiber expansion joints have been made by saturating fiberboard in anasphalt/solvent solution, allowing the asphalt solvent mixture to beabsorbed into the fibers, and allowing the solvent to evaporate. Fiberexpansion joints have also been made by adding solid asphalt particlesinto a slurry of fibers. The asphalt particles are dispersed in thefiber slurry by mechanical mixing, and the slurry is dewatered, pressedinto a board and dried.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates to a process for manufacturing fiberboardincluding the steps of preparing a fiber slurry mixture by adding amaterial containing cellulose fibers to water and agitating the fiberslurry mixture and transferring the fiber slurry mixture to a spraychamber. Then a bituminous material, such as asphalt, is heated to atemperature between 300 and 440 degrees F., wherein the bituminousmaterial is in a liquid state. The liquid bituminous material isatomized within the spray chamber by mixing it with a pressurized gas,such as compressed air, forming a mist comprising droplets of bituminousmaterial having a diameter between 20 microns and 50 microns. A waterspray solidifies the bituminous material droplets thereby formingbituminous particles which fall into the fiber slurry within the spraychamber. From there the slurry is sheared, dewatered, and dried, forminga finished fiberboard.

The present disclosure also relates to a process for atomizing abituminous material, such as asphalt, to produce solid particles rangingin size from 20 microns to 50 microns. A bituminous material is heatedto a temperature between 300 and 450 degrees F., wherein the bituminousmaterial is in a liquid state. The liquid bituminous material isatomized by mixing the liquid bituminous material with a gas, such ascompressed air, by passing each through a nozzle. The gas is supplied ata pressure between 10 psi and 50 psi, but preferably between 20 psi and40 psi and a temperature between 200 degrees F. and 300 degrees F.Mixing the liquid bituminous material and the compressed gas produces amist of bituminous droplets having a diameter between 20 microns and 50microns. A water spray having a temperature between 40 degrees F. and 60degrees F., but preferably between 45 degrees F. and 55 degrees F. isapplied to the bituminous mist, solidifying the bituminous materialdroplets and thereby forming bituminous particles having a diameterbetween 20 microns and 50 microns.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The present disclosure will be described hereafter with reference to theattached drawings which are given as a non-limiting example only, inwhich:

FIG. 1 is a schematic representation of the process of the presentdisclosure;

FIG. 2 is a schematic representation of the spray tank of the presentdisclosure;

FIG. 3 is a section view of an asphalt spray nozzle;

FIG. 4 is an end view of the nozzle shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The process for manufacturing an asphalt-impregnated fiberboard of thepresent disclosure introduces fine asphalt particles into a fiber slurryby atomizing molten asphalt and spray cooling the atomized asphalt. Theasphalt particles may then be added directly to the fiber slurry orstored for later use.

Referring now to FIG. 1, a fiber slurry is prepared in a pulper 10 byadding material containing cellulose fibers, such as wood pulp, sugarcane, switch grass, straw, recycled paper pulp, or other cellulosecontaining organic material to water. A mixer 12, agitates the fiberslurry, maintaining the fibers in suspension. The fiber slurry istransferred to a pulp chest 14 where it is held while awaiting furtherprocessing, depending on production parameters. Depending on theapplication, a pump 16 may be used to transfer the fiber slurry from thepulper 10 to the pulp chest 14. Alternatively, the fiber slurry may betransferred by gravity into the pulp chest 14.

Asphalt is heated in a tank 20 to a temperature between 300 and 440degrees F. At this temperature, the asphalt is in a liquid phase andflows freely. From the tank 20, a pump 22 transfers the molten asphaltthrough a filter to remove any impurities such as solids or coking thatmay have formed during the heating process. A heater 26 is provided tofurther heat the molten asphalt to a temperature between 400 and 450degrees F. The heater 26 also provides heat to the piping carrying themolten asphalt to the spray chamber 30.

In an exemplary embodiment, the heater 26 is a shell and tube heatexchanger having hot mineral oil on the shell side and the moltenasphalt on the tube side. The heater maintains mineral oil at atemperature of approximately 600 degrees F. The mineral oil iscirculated within the shell side of the heater, transferring heat to themolten asphalt as it passes through the tube side of the heater. Theasphalt transfer piping 28 is constructed of double lumen pipe, whereinthe heated oil circulates through an outer lumen to maintain thetemperature of the molten asphalt as it is flows through an inner lumenas it is transferred from the asphalt tank to the spray chamber.

Referring now to FIG. 2, the spray chamber 30 includes a housing 32,enclosing an atomization head 34. The atomization head 34 includes aplurality of asphalt nozzles 36. Each nozzle is connected to the asphaltpiping 28. In an exemplary embodiment, a pump 38 is connected in-linewith each nozzle 36 for metering the flow of asphalt. Each nozzle 36 isalso connected to a pressurized air manifold 40.

An air compressor, 42 supplies a source of compressed air which is driedand heated to a temperature between 200 degrees F. and 300 degrees F.The dried compressed air is provided to each nozzle 36 through asolenoid valve 44. The solenoid valve 44 allows the compressed air to beapplied to only those nozzles 36 in use providing bitumen to the slurryin the spray chamber 30. The compressed air may be provided at apressure between 10 psi and 50 psi. In an exemplary embodiment, thecompressed air is provided at a pressure of between approximately 20 psiand 40 psi. It has been found that moist air causes the molten asphaltto solidify prematurely, resulting in clogging of the nozzles. It istherefore desirable that the compressed air be passed through a suitablecommercially available air dryer before it is introduced into theprocess.

Referring to FIGS. 3 and 4, each nozzle 36 includes a body 46 having aliquid passage 48, through which molten asphalt flows, surrounded by aplurality of gas passages 50, which provide pressurized air as shown inFIGS. 3 and 4. The liquid passage 48 and the gas passages 50 dischargeinto an atomization chamber 52. The liquid passage 48 may be locatedalong the longitudinal axis of the nozzle body 46 and gas passages 50symmetrically disposed about liquid passage 48. Such a nozzle design isshown in U.S. Pat. No. 6,997,405 which is herein incorporated byreference. The atomization chamber 52 is configured to combine themolten asphalt and the pressurized air to produce an asphalt mist 54.The atomization chamber 52 includes a conical wall 53 having an angle φwhich may be varied depending on the desired atomization pattern. In anexemplary embodiment of the present disclosure, the atomization chamber54 has a wall angle φ of 45 degrees, which produces a conical spraypattern having a vertex angle of 45 degrees. The atomized asphalt mist54 is discharged from atomization chamber 54 as liquid asphalt dropletshaving a diameter of approximately 20 to 50 microns. The size of theasphalt droplets may be varied by adjusting the air pressure. Generally,higher air pressure produces atomized asphalt having a smaller particlesize.

The spray chamber 30 shown in FIG. 2 depicts five spray nozzles forclarity. However, in an exemplary embodiment of the present disclosure,the spray chamber 30 includes a spray head 34 having twelve spraynozzles 36. Each spray nozzle is designed for an asphalt flow rate of 1gal/min. Having solenoid valves controlling the asphalt flow toindividual nozzles allows for varying the asphalt flow rate depending onthe desired production rate and/or asphalt concentration for thefinished product. For example, the amount of asphalt added to the fiberslurry may be adjusted from about 1 gal/min, with a single solenoidvalve open at a minimum production rate to about 12 gal/min at highproduction rates. Also, the number of nozzles in operation may be drivenas a function of the desired asphalt content in a finished product.

The spray chamber 30 also includes a plurality of water spray heads 56arranged proximate to the discharge of the asphalt nozzles 36. The waterspray heads 56 are connected to a supply of chilled water maintained ata temperature of approximately 40 degrees F. to 60 degrees F. In anexemplary embodiment of the present disclosure, the chilled water isprovided at a temperature between 45 degrees F. and 55 degrees F. Thespray heads 56 are configured to direct a water mist towards theatomized asphalt discharge at a spray angle θ of approximately 45degrees downward. The chilled water mist solidifies the molten dropletsof the atomized asphalt mist, forming solid asphalt particles having asize of 20 to 50 microns.

A pulp supply line 58 connects the pulp chest 14 to the spray chamber30. A slurry feed pump 60 is provided in the pulp supply line 58 totransfer the fibrous material slurry from the pulp chest 14 to the spraychamber 30. The slurry feed pump 60 may be of variable speed andconnected to a control system (not shown) to accommodate variableproduction throughput.

The fibrous material slurry is pumped into the spray chamber 30 to apredetermined level 62. As the molten asphalt mist 54 is cooled and theasphalt droplets solidify, fine asphalt particles drop into the fibrousmaterial slurry in the bottom of the spray chamber 30. One or moremechanical mixers 64 agitate the fibrous material slurry, maintaining ahomogeneous mixture of fibers and asphalt particles.

The slurry in the spray chamber 30 should contain about 8% weight toabout 10% weight fiber or solid content. The slurry should also containabout 10% weight to about 30% weight asphalt.

A discharge pump 66 is connected to the outlet of the spray chamber 30and directs the slurry to the next step in the process. The dischargepump 66 may be coordinated with the fibrous slurry feed pump 60 tomaintain a predetermined slurry level and dwell time within the spraychamber 30.

From the spray chamber 30, the slurry is transferred to a refiner 68where the slurry is sheared by a series of mixing plates. The mixingplates are mounted on a shaft and rotate relative to each other. As theslurry flows through the refiner, it passes between the mixing plates,shearing the slurry and in the process shredding the fibrous material.The shredding of the cellulose fibers forms a large amount of surfacearea for interaction with and dispersion of the asphalt particles,allowing for even distribution of the asphalt particles throughout thefibers.

Additional ingredients may be added to the slurry including waxes,starches, alum, and other fillers and agents. These additionalingredients and fillers may be added at any point in the process priorto dewatering where they will become intermixed with the othercomponents, as is known in the art. For example a wax, such as paraffin,may be added to the slurry in a concentration of about 1.0% weight toabout 2.5% weight; starch may be added in a concentration of about in aconcentration of about 1.0% weight to about 3.0% weight; and aluminumsulfate may be added in a concentration of about 1.0% weight to about2.0% weight.

In an alternative embodiment of the present disclosure, a dye may beadded to the slurry before drying. The dye serves to color the fibrousmaterial to produce an evenly colored finished fiberboard improving theaesthetic appearance of the fiberboard. The addition of a dye, alsoserves to regulate the pH of the slurry. The dye should have a pH ofabout 6 to about 8. It has been discovered that a slurry having a pH ofapproximately 6.8 has been found to promote better adhesion of theasphalt particles to the cellulose fibers, and thus improveddistribution of asphalt throughout the finished fiberboard. The dye maybe a generally commercially available water-based dye. Alternatively, asolvent based dye may be used. However, a solvent-based dye containsvolatile compounds which may be harmful to the environment and which maypresent the risk of fire or explosion when subjected to heat whiledrying.

A slurry transfer pump 70 pumps the slurry mixture from the refiner 68to a ready chest 72 where it is held for dewatering. Another transferpump 74 pumps the slurry from the ready chest 72 to a Fourdrinier-typepress 76 as is commonly known in the art, where the slurry is dewateredand formed into a wet fiber mat.

After the dewatered wet mat leaves the Fourdrinier press 76, the matpasses through a shear 78 where it is cut before being fed into a dryer80. The mat is dried for approximately 1-3 hours depending on itsphysical characteristics. The finished fiberboard preferably should haveabout 10% weight to about 40% weight total asphalt content and less thanabout 3% total moisture content. After being dried, the fiberboard maypass through a second shear 82 again be cut to a commercially desirablesize. The finished fiberboard may then be stacked 84 for furtherprocessing or for shipment.

Alternatively, an additional coating of asphalt or other petroleum fluidmay be applied to the outer surface of the fiberboard to provideadditional resistance to moisture penetration. A coater 86 applies byroller the additional coating to the major surfaces of the fiberboard.For example, a commercially available hot melt double-sided rollercoater manufactured by the Black Bros. Co. may be used. Fluids such asflux oil or fuel oil, in addition to asphalt, have been found to resistwater penetration into the finished fiberboard.

Although ASTM D 1751-04 specifies that the finished fiber board have anasphalt content of at least 35.0% weight, a number of tests werepreformed on fiber boards manufactured by the process of the presentdisclosure, varying the % weight of asphalt. For example, anasphalt-impregnated fiberboard manufactured by the process of thepresent disclosure containing 15% weight asphalt was tested according toASTM Method D 545. The results are summarized in Table 1 below:

TABLE 1 asphalt content 15% weight Property Test Results ASTM 1751-04Compression (psi) 150 Pass Extrusion (in.) 0.30 Fail Recovery (%) 65Fail Density (lb./cu. Ft.) 20 Pass Water absorption 24 Fail

A second test was performed on a fiberboard containing 25% weightasphalt content. The results are summarized in Table 2 below:

TABLE 2 asphalt content 25% weight Property Test Results ASTM 1751-04Compression (psi) 350 Pass Extrusion (in.) 0.25 Pass Recovery (%) 75Pass Density (lb./cu. Ft.) 21 Pass Water absorption (volume %) 19 Fail

A third test was performed on a fiberboard containing 35% weight asphaltcontent. The results are summarized in Table 3 below:

TABLE 3 asphalt content 35% weight Property Test Results ASTM 1751-04Compression (psi) 540 Pass Extrusion (in.) 0.15 Pass Recovery (%) 78Pass Density (lb./cu. Ft.) 22 Pass Water absorption (volume %) 12 Pass

The process of the present disclosure allows introduction of very fineasphalt particles into the fibrous slurry mix. It has been discoveredthat small asphalt particle size allows for better dispersion of theasphalt throughout the fibers and increased bonding between asphalt andfiber. Thus a fiberboard may be produced exhibiting improvedcharacteristics over asphalt-impregnated fiberboards produced by methodspresently known in the art.

While this disclosure has been described as having exemplaryembodiments, this application is intended to cover any variations, uses,or adaptations using the general principles set forth herein. It isenvisioned that those skilled in the art may devise variousmodifications and equivalents without departing from the spirit andscope of the disclosure as recited in the following claims. Further,this application is intended to cover such departures from the presentdisclosure as come within the known or customary practice within the artto which it pertains.

The invention claimed is:
 1. A process for producing bituminousparticles by atomizing a molten bituminous material comprising the stepsof: heating a bituminous material to a temperature such that thebituminous material is in a liquid state; passing the liquid bituminousmaterial through a nozzle, the nozzle having a liquid passage and aplurality of gas passages, and an atomization chamber, wherein theliquid bituminous material and a pressurized gas provided through theplurality of gas passages are mixed together within the atomizationchamber forming a mist of liquid bitumen droplets wherein the liquidbitumen droplets have a diameter of between approximately 20 microns andapproximately 50 microns; and allowing the liquid bitumen droplets toenter a slurry and solidify in the slurry.
 2. The process of claim 1,wherein the bituminous material is heated to a temperature between 300to 400 degrees Fahrenheit.
 3. The process of claim 2, further includingthe step of additionally heating the bituminous material to atemperature of between 400 to 450 degrees Fahrenheit.
 4. The process ofclaim 2, wherein the bituminous material is atomized by mixing with agas having a pressure of between approximately 10 psi and 50 psi.
 5. Theprocess of claim 2, wherein the bituminous material is atomized bymixing with a gas having a pressure of between approximately 20 psi and40 psi.
 6. The process of claim 4, wherein the pressurized gas iscompressed air.
 7. The process of claim 6, wherein the compressed air isa dried compressed air.
 8. The process of claim 6, wherein thecompressed air is heated to a temperature between 200 degrees Fahrenheitand 300 degrees Fahrenheit.
 9. The process of claim 1, wherein thebituminous material is asphalt.
 10. The process of claim 1, wherein theprocess further comprises the step of drying the pressurized gas. 11.The process of claim 10, wherein the drying step of the pressurized gasoccurs prior to the introduction of the gas into the plurality of gaspassages.
 12. The process of claim 1, wherein the atomization chambercomprises at least one conical wall having at least one wall angle ø.13. The process of claim 12, wherein the at least one wall angle ø maybe varied depending upon a selected atomization spray pattern.
 14. Theprocess of claim 13, wherein the selected atomization spray pattern is aconical atomization spray pattern and the wall angle ø is 45 degrees.15. The process of claim 14, wherein the conical atomization spraypattern has a vertex angle of 45 degrees.
 16. The process of claim 1,wherein the bituminous material is asphalt.
 17. The process of claim 16,wherein the asphalt is a natural asphalt.
 18. The process of claim 16,wherein the asphalt is a synthetic or non-natural asphalt.
 19. Theprocess claim 1, further comprising the step of adding a dye to theliquid bituminous material.
 20. The process claim 1, wherein thesolidified bitumen particles have a diameter of between approximately 20microns and approximately 50 microns.
 21. Bituminous particles producedby the process of claim
 1. 22. The bituminous particles claim 21,wherein the bituminous material is asphalt.
 23. The bituminous particlesclaim 22, wherein the asphalt is a natural asphalt.
 24. The bituminousparticles claim 22, wherein the asphalt is a synthetic or non-naturalasphalt.